I might be able to help you port it to C, but I'm sure you can find more accomplished C/C++ programmers to do it. Try also posting this at someplace like rpgdx.net, there's a lot of C/C++ and BASIC hobbyists there.

The result would be a single executable file, which contains all the code, data and JISC interpreter.

The reason for JISC is to give JBASIC the ability to have an interpreter.
One of the key selling points of and BASIC compiler is in fact interpretation. I believe once JISC is ported to C/C++ or ASM that the run time speed will rival that of QB45.

If speed proves to be an issue then this project could be taken one step
further. A JISC x86 Compiler could also be developed. It should be relativly easy to generate x86 code from JISC compared to generateing x86 code directly from JBASIC.